Number of distinct values of a variable into summary statistics

[Aiko Schmeisser]

Hi everybody.

My dataset has panel data at the subnational level of regions. In my summary statistics I do not only want to include the number of observations for every variable, but also the corresponding number of regions and countries where the variables have nonmissing values.

I can display the number of regions for a variable by
distinct REGION if VARIABLE !=.
But I want to include this number into the summary statistics for this variable.

My idea was to create a summary statistics "by hand" using reshape and egen rowmean/rowmedian/etc. commands. But I don´t know how to include the number of distinct values of the variable REGION and COUNTRY for nonmissing values of the variables.


Thanks for your help!

Aiko Schmeisser

[Nick Cox]

distinct is a user-written program from the Stata Journal, as you are asked to explain (FAQ Advice #12).

search distinct in Stata brings up clickable links. I've edited the output below, but anyone interested should

1. use the latest link to download program and help file

2, use the link to the 2008 paper to get a discussion of the problem.

. search distinct, sj

Search of official help files, FAQs, Examples, SJs, and STBs

SJ-15-3 dm0042_2  . . . . . . . . . . . . . . . . Software update for distinct
        (help distinct if installed)  . . . . . .  N. J. Cox and G. M. Longton
        Q3/15   SJ 15(3):899
        improved table format and display of large numbers of
        observations

SJ-12-2 dm0042_1  . . . . . . . . . . . . . . . . Software update for distinct
        (help distinct if installed)  . . . . . .  N. J. Cox and G. M. Longton
        Q2/12   SJ 12(2):352
        options added to restrict output to variables with a minimum
        or maximum of distinct values

SJ-8-4  dm0042  . . . . . . . . . . . .  Speaking Stata: Distinct observations
        (help distinct if installed)  . . . . . .  N. J. Cox and G. M. Longton
        Q4/08   SJ 8(4):557--568
        shows how to answer questions about distinct observations
        from first principles; provides a convenience command

distinct doesn't include a generate() option. That's partly because the 2008 paper shows that egen functions (your instinct was right) were already available to do this.

You don't give example data, but this silly example shows some technique.

. sysuse auto, clear
(1978 Automobile Data)

. bysort foreign : distinct rep78

------------------------------------------------------------------------------
-> foreign = Domestic

------------------------------
       |     total   distinct
-------+----------------------
 rep78 |        48          5
------------------------------

------------------------------------------------------------------------------
-> foreign = Foreign

------------------------------
       |     total   distinct
-------+----------------------
 rep78 |        21          3
------------------------------

. egen tag = tag(rep78 foreign)

. egen ndistinct = total(tag), by(foreign)

. tabdisp foreign, c(ndistinct)

----------------------
 Car type |  ndistinct
----------+-----------
 Domestic |          5
  Foreign |          3
----------------------